Determining the Effects of the Pathogenic Developmental and Epileptic Encephalopathy Patient Variant, scn1b-p.r98c, on Neuronal Excitability
Abstract number :
1.033
Submission category :
1. Basic Mechanisms / 1C. Electrophysiology/High frequency oscillations
Year :
2024
Submission ID :
1307
Source :
www.aesnet.org
Presentation date :
12/7/2024 12:00:00 AM
Published date :
Authors :
Presenting Author: Amanda Catalfio, PhD – University of Michigan Medical School
Daniel Kashima, MD, PhD – University of Michigan Medical School
Chunling Chen, MD – University of Michigan Medical School
Lori Isom, PhD – University of Michigan-Ann Arbor
Rationale: Dravet syndrome (DS) is a devastating developmental and epileptic encephalopathy (DEE). DS patients develop symptoms within the first year of life including pharmacoresistant and febrile seizures, profound intellectual disability, cognitive decline, movement disorders, and increased mortality due to sudden unexpected death in epilepsy (SUDEP). Inherited biallelic variants in SCN1B, encoding voltage gated sodium channel (VGSC) b1/b1B subunits, have been linked to DS and to the clinically more severe early infantile DEE (EI-DEE). VGSCs are responsible for the initiation and propagation of action potentials in neurons. VGSC b1 subunits non-covalently associate with VGSC α subunits and modulate channel expression, trafficking, and voltage dependent properties. A pathogenic biallelic variant in SCN1B, SCN1B-c.265C >T predicting p.R89C, was identified in two children of a non-consanguineous family. One child was diagnosed with DS, while the other had a milder epilepsy phenotype. We then identified an unrelated biallelic SCN1B-c.265C >T patient with EI-DEE (Brain Commun 2023; 5(6); 283). In heterologous cells, b1-R89C differentially regulates VGSC a subunits, increasing Nav1.6-mediated sodium current density, but not that of Nav1.1, suggesting differential regulation in vivo (Brain Commun 2023; 5(6); 283). However, the impacts of SCN1B-p.R98C on neuronal function in vivo have not been investigated.
Methods: Scn1b-p.R98C mice were previously generated using CRISPR-Cas9 gene editing (Brain Commun 2023; 5(6); 283). Homozygous animals exhibit increased susceptibility to hyperthermia induced seizures at postnatal day (P) 15, 100% expression of spontaneous generalized seizures by P30, and ~20% undergo SUDEP by approximately P60 (Brain Commun 2023; 5(6); 283). Here we examined the neuronal phenotype of P17-28 male and female Scn1b-p.R89C mice. We used whole-cell patch clamp electrophysiology approaches to measure effects of the variant on passive membrane properties, intrinsic excitability, and single action potential properties of parvalbumin positive (PV+) interneurons and pyramidal neurons in layers 5/6 of the somatosensory cortex and CA1 region of the hippocampus. Wild-type littermates were used as controls.
Results: Our results show no differences between genotypes in any measure for somatosensory cortical PV+ interneurons or pyramidal neurons. In the CA1 region of the hippocampus, we found no differences for any measure in PV+ interneurons. In contrast, CA1 pyramidal neurons were hyperexcitable, however, with no changes in passive membrane properties or single action potential properties.
Conclusions: These results suggest that the Scn1b-p.R98C variant may confer cell type and brain region specific changes in neuronal excitability in vivo. Ongoing studies are examining potential effects of Scn1b-p.R98C heterozygosity on neuronal function as well as the effects of Scn1b-p.R98C homozygosity and heterozygosity on synaptic transmission.
Funding: NIH R37 NS076752 (LLI), T32 TR004764 (AMC)
Basic Mechanisms